A safety lockout system for releasably locking a mast guided working surface to a mast is provided. The safety lockout system may include an outer rollcase, an inner rollcase, and a lockout assembly. The lockout assembly includes a retractable dog that is movable between an engaged position and a disengaged position. The lockout assembly may include a dog release device that operates both manually and automatically to move the retractable dog from the disengaged position to the engaged position. Automatic operation of the dog release device is triggered when the working surface experiences a tilted condition. A dog emergency release device may be provided to manually move the retractable dog to the disengaged position in the event of a malfunction. The lockout assembly may include a lockout assembly locking device that allows a portion of the lockout assembly to fold up and move the retractable dog to the disengaged position.